1. Field of the Invention
The present invention relates to a cross color noise reduction and contour correction apparatus in NTSC (National Television System Committee) color television image processing system.
2. Description of the Prior Art
As a conventional contour correction apparatus, "Vertical and Horizontal Aperture Equalization" disclosed in U.S. Pat. No. 3,546,372 is known.
FIG. 1 is a block diagram showing an arrangement of this type of contour correction apparatus.
This apparatus first synthesizes output signals from respective 1H delay circuits (one horizontal scanning time delay circuits) 1 and 2, secondly produces a contour signal by synthesizing output signals from the 1H delay circuits by a contour correction signal generating circuit 3, and thirdly adds the contour signal to R, G and B signals, respectively, by mixers 4, 5 and 6.
The output signals from the mixers 4, 5 and 6 are synthesized to a luminance signal in accordance with the NTSC system or the like by a luminance signal synthesizer circuit (Y matrix) 7, and the synthesizer luminance signal is outputted from an amplifier 11. Color difference synthesizing circuits 8 and 9 produce color difference signals in accordance with the NTSC system or the like. The color difference signals are modulated by a color difference signal modulator 10 into a carrier chrominance signal (this signal is also called a "color difference signal" in general), and is produced from an amplifier 13. A mixing amplifier 12 mixes the luminance signal and the carrier chrominance signal, and produces a composite color signal to the outside.
The conventional apparatus corrects contours by the "Out of Green" method, which corrects contours by adding to the RGB signals the contour correction signal produced on the basis of the G signal of the RGB signals. As a result, the RB signals must be delayed in accordance with the G signal so that the delay time of the RB signals becomes equal to the delay time of the G signal passing through the contour correction circuit 3. This timing (phase) adjustment between the RGB signals is very difficult, particularly, when the "pixel shift" is performed with a CCD camera, which restricts its capability. Furthermore, the contour correction (contour emphasis) with regard to the PB signals has little effect as shown in FIG. 2 (portions indicated by broken circles in FIG. 2 cannot be contour corrected) because the contour correction signal is formed only from the G signal.
To solve such problems, another contour compensation circuit is proposed in Japanese patent Application Laying-Open No. 63-90283. This apparatus computes the intensity ratios of the RGB signals, adds the RGB signals weighted in accordance with the ratios, and generates a contour compensation signal according to the result of the addition. Although the apparatus can solve the above problems, it has a drawback that the circuit configuration is complicated.
On the other hand, with regard to the reduction of cross color noises, the apparatus described in U.S. Pat. No. 4,893,176 is known. This apparatus reduces cross color noises, i.e., the interference between the luminance signal and the chrominance signal by using a comb filter.
To accomplish the contour correction described in U.S. Pat. No. 3,546,372, and the cross color noise reduction described in U.S. Pat. No. 4,893,176 at the same time, at least five 1H delay circuits are required: two 1H delay circuits 1 and 2 in FIG. 1; at least two 1H delay circuits included in the comb filter for reducing cross color noises; and one 1H delay circuit for adjusting the phases of the luminance signal and the chrominance signal (this 1H delay circuit corresponds to the 1H delay circuit 18 in FIG. 3, which will be described later).